Visual fire warning system

ABSTRACT

A FIRE WARNING SYSTEM IS MOUNTED ON THE BACK OF A LIGHT SWITCH PLATE AND INCLUDES A CURRENT ACTUATED INTERRUPTER CONNECTED BETWEEN THE CURRENT SUPPLY AND THE LIGHT SWITCH. A THERMAL SENSITIVE SWITCH IS CONNECTED TO THE INTERRUPTER AND LIGHT SWITCH AND NORMALLY SHORTS THE INTERRUPTER SO THAT THE LIGHT AND SWITCH FUNCTION NORMALLY. IN AN ALARM CONDITION, THE THERMAL SWITCH CONNECTS THE LIGHT TO THE CURRENT SOURCE THROUGH THE INTERRUPTER SO THAT THE LIGHT FLASHES ON AND OFF RAPIDLY TO PROVIDE A VISUAL ALARM AND AROUSE ANY SLEEPING OCCUPANTS OF THE ROOM IN DANGER OF FIRE.

' US. Cl. 340-228 United States Patent ABSTRACT OF THE DISCLOSURE A fire warning system is mounted on the back of a light switch plate and includes a current actuated interrupter connected between the current supply and the light switch. A thermal sensitive switch is connected to the interrupter and light switch and normally shorts the interrupter so that the light and switch function normally. In an alarm condition, the thermal switch connects the light to the current source through the interrupter so that the light flashes on and off rapidly to provide a visual alarm and arouse any sleeping occupants of the room in danger of fire.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to control means for generating a visual alarm in a fire warning system. More particularly, one embodiment of the invention concerns a fire warning apparatus which is mounted upon and integral with an electric light switch plate and therefore capable of being economically installed in the interior of buildings.

In the design of residential fire alarms, it has been a problem to provide a system which would ellectively awaken a sleeping occupant of a room 'when a danger of fire exists. Although buzzers and other audible alarms are used, they are not always elfective with sound sleepers or with persons who are hard of hearing and audible alarms are completely ineffective with a deaf person.

Other attributes of a satisfactory home fire warning system is that it should be inexpensive and easily installed with a minimum of labor.

(2) Description of the prior art In the past, a number of easily installed home fire warning systems have been proposed. For example, in Pat. No. 3,320,601, issued to A. M. Yankus, it is demonstrated that an audible fire alarm may be mounted upon the wall plate of an electrical outlet receptacle or a light switch plate. However, as is pointed out above, fire warning systems employing only audible alarms possess serious, inherent disadvantages.

Visual indicator lamps have long been used in prior fire warning systems to indicate an alarm condition. Further, Pat. No. 3,054,994, issued to A. C. Haram, discloses a control device for using a conventional table lamp as an indicator that an audible alarm is being actuated. A relay and switch arrangement is employed to change the lamp from off to on or vice versa concurrently with a signal from an audible indicator, such as a doorbellQHowever, the Haram device possesses the disadvantages of a relatively complex and expensive apparatus and is not adapted as a visual alarm for arousing person who is asleep.

SUMMARY OF THE INVENTION In one embodiment of the invention, a fire warning system is adapted to be connected to a source of current, an electric light and a light switch. A current actuated interrupter is connected between the current source and the light switch. A thermal responsive switch is con- 3,555,531 Patented Jan. 12, 1971 nected to the current source and the light switch so that when the thermal switch is normal the interrupter is bypassed and the light operates normally under control of the light switch. However, when a fire alarm condition exists the thermal switch closes and connects the light to the current source through the interrupter so that the light flashes on and oil rapidly to attract attention and arouse any sleeping occupants of the room in danger.

BRIEF DESCRIPTION OF THE DRAWING The nature of the present invention and its various advantages will appear more fully by referring to the following detailed description in conjunction with the appended drawing, in which:

FIG. 1 is a front elevational view of and typical installation of a fire warning device of the present invention;

FIG. 2 is a sectional view taken substantially through a plane indicated by section line 22 in FIG. 1;

FIG. 3 is a sectional view taken substantially through a plane indicated by section line 3--3 in FIG. 1;

FIG. 4 is a perspective view of a type of current actuated interrupter as may be employed in the invention;

FIG. 5 is a circuit diagram of a fire warning device of the present invention; and

FIG. 6 is a sectional view of an audible alarm of a type which may be used in an embodiment of the invention.

DETAILED DESCRIPTION Refering to FIGS. 1, 2 and 3, it can be seen that the fire warning system of the invention may be arranged for mounting on an interior wall 10 provided with an opening in which is positioned a metal power box or enclosure 11. The power box is mounted in accordance with well known practices of electrical construction and wiring, for example, by securing to a wall stud 12. The box 11 is of a commercially available type provided with openings for receiving a pair of electrical cables 13 and 14. Each cable 13 and 14 contains a pair of electrical wires 15, 16 and 17, 18, respectively. The wire 17 leads to a terminal 8 on a single-pole, single-throw light switch 19 while wire 16 is connected to a current actuated interrupter 33, and a normal terminal 29 of a thermal actuated switch 26 by a splice 30. Alternatively, a third insulated terminal may be provided for interconnecting the wires in lieu of the splice. Wires 15, 18 are connected together by a splice 20. The light switch 19' is similar to those which are commercially available and wherein actuation of the switch connects terminal 8 to terminal 9. The cable 13 is connected to a source of electric current and the cable 14- is connected to the electric lamp in the room which is under control of the switch 19.

The light switch 19 is mounted to the power box 11 by a pair of screws 2121 which also secure a switch plate 22 which covers the face of the switch 19. The switch plate has a conventional opening in the center to allow the actuation handle 23 of the switch 19 to protrude. The switch plate 22 also has, to one side of the central aperture, a single circular opening 24 surrounded by a plurality of smaller openings 25-25. The openings 25-25 are positioned to overlie a thermal sensing unit 26 mounted on the side of the switch 19. The thermal sensor 26 includes a conventional bimetallic strip 27 which is connected at one end to an anchor terminal 28. The bimetallic strip 27 is positioned so that over the range of normal room temperatures, the strip is in contact with a normal terminal 29 which is connected to the incoming power wire 16 at the splice 30. When the temperature of the strip 27 is elevated to a level to indicate danger of fire, the strip flexes into contact with an alarm terminal 31. The anchor terminal 28 is connected to the interrupter 33 and the 3 switch terminal 9. A test button 32 is provided through the opening 24 so that an alarm condition may be manually simulated to test the system by bending the bimetallic strip 27 into contact with the alarm terminal 31. An audible alarm 34, such as a buzzer may also be connected in parallel with the flasher unit 33.

The flasher or interrupter unit 33 can be of a number of diflerent arrangements, for example, an inexpensive current actuated interrupter such as the type shown in FIG. 4 may be used. The flasher 33 includes an insulative substrate 35 upon which is mounted a first, fixed contact 36 which is connected to a first terminal 37. Also mounted upon the substrate 35 is a conventional bimetallic strip 38 having a second, movable contact 39 on one end and a second terminal 41 on the other end. A plurality of turns of high resistance electrical wire 42 is wound around the strip 38 and opposite ends of the wire are connected to the terminal 41 and the contact 36, respectively. Normally, when no voltage is being applied between terminals 37 and 41, the bimetallic strip 38 is at room temperature and the strip is positioned so that contacts 36 and '39 are not in contact. However, when a sufficient voltage is placed across terminals 37 and 41, current is caused to flow through the resistance wire 42 which heats the bimetallic strip 38 and causes it to flex so that contacts 36 and 39 close and shunt out the resistance windings 41. The bimetallic strip 38 cools, the contacts 36 and 39 are opened and the cycle repeats itself at a frequency determined by the design of the flasher. During the period when the contacts 36 and 39 are closed, comparatively large amounts of current may be carried between terminals 37 and 41, for example to illuminate a lamp, while very little current is conducted through the resistance wire 42 while the contacts 37 and 41 are open.

In operation, the circuit functions as shown in FIG. 5. A source of alternating electric current is connected to the input wires and 16. One side of the input line, wire 16, is connected to the normal terminal 29 of the thermal sensor 26 and then to the bimetallic strip 27 through the flasher unit 33. The buzzer 34 is connected in parallel with the flasher 33. The anchor terminal 28 of the thermal sensor 26 is connected to one side of the switch 19 which contains moving contacts 43. The output side of the moving contact 43 is connected to a conventional lamp 45 providing illumination for a room under control of the switch 19.

When the switch 19 is open, there is no path between the wires 15 and 16 so the lamp 45 is dark. When the switch 19 is closed, current flows from wire 16 through contact 29, the bimetallic strip anchor contact 28, contact 43, the lamp 45, and wire 15 to illuminate the lamp in a normal fashion. Current does not flow through the windings of the flasher 33 or buzzer 34 because of their much greater resistance, typically one thousand ohms each, in comparison with the thermal sensor path, which is essentially less than one ohm.

If a fire alarm condition develops while switch 19 is closed and lamp 45 is illuminated, for example a person falling asleep while reading and smoking, the bimetallic strip 27 is heated through the apertures in the switch plate 25 and flexes into contact with the alarm terminal 31. Current is now forced to flow through the windings of the flasher 33 and as its contacts alternately open and close at a preselected rate, the lamp is flashed on and off. After a period of such flashing of the lights in the room, even a sound sleeper may be annoyed into wakefulness. In addition, during the periods that the lamp 45 is dark, the buzzer 34 is sounded to provide an audible stimulus to the occupant of the room.

If a fire alarm condition develops while switch 19 is open and lamp 45 is dark, the bimetallic strip is heated and flexes into contact with the alarm terminal 31 so that current flows from wire 16, through the flasher winding, anchor contact 28, the bimetallic strip 27, alarm contact 31, Wire 17, the lamp 45 and wire 18, 15. The flasher again functions to turn the room illumination on and off to visually indicate an alarm condition and arouse any sleeping occupants of the room while the buzzer 34 sounds in alternation with the flickering of the light.

A further embodiment of the invention is that of a sounder which may be advantageously employed with the metal power box 11, as shown in FIG. 6. A non-conducive cylindrical sleeve 46- is attached to the body of the switch 19 so that its axis is perpendicular to the bottom surface of the power box 11. A shaft 47, formed of a metal having a relatively high magnetic susceptability and having a diameter smaller than the inside diameter of the sleeve 46, is positioned within the sleeve so that the end of the shaft engages the bottom surface of the power box 11. A helical spring 48 biases the shaft into engagement with the metal wall of the box. A conductor 49 is wound around the sleeve 46 and connected between the anchor contact 28 and the lower contact terminal of the switch 19 just as the buzzer 34 is shown connected in FIG. 2. referring again to FIG. 6, when the winding 49 is energized with an alternating current the shaft 47 is alternately driven into and away from contact with the bottom surface of the metal box 11 at the frequency of the current. A loud audible noise is generated to indicate a fire alarm and if the metal box 11 is connected through the building by means of metal wiring conduit 50 as is often the case, the noise is transmitted through the conduit network to alert others in various parts of the building.

The novel installational arrangement of the instant fire Warning system may be easily located in various rooms of a home or in a hotel and motel rooms since each will almost always be equipped with a wall mounted light switch. Further, the warning system employs the normal illumination of a room as a visual alarm and thereby eliminates the need for installing other visual indicators. In addition to the installational advantages inherent in the fire *warning devices of the present invention, it may be utilized with very little modification or expense since existing parts and devices through which electrical power is distributed to a room are employed.

It should be apparent that the essential features of the invention may be employed in other embodiments than with a wall mounted switch plate. For example, the circuit shown in FIG. 5 is equally adaptable for mounting in the base of a table lamp wherein the switch 43 would be the existing on-off switch of the lamp. This embodiment is particularly useful in sleeping rooms, such as in a hotel and motel, which usually have bedside reading lamps. It is to be noted that the invention will also serve to attract the attention of passersby to an alarm condition in an unoccupied house since the flashing light may be seen through the windows of the house. Additionally, an external lamp, controlled by an internal switch, such as a porch light, may be used to alert others to an alarm condition existing within a house.

The foregoing is considered as only illustrative of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed is: 1. In a fire warning device adapted to be connected to a source of electric current, an electric lamp, and a control switch for connecting the source to the lamp thermal responsive switch means, said switch being in a normally open state and capable of moving to a closed state in response to an environmental temperature indicative of a fire alarm condition;

current actuated interrupter means connected between said source of electric current and said control switch; and

means connecting said thermal responsive switch means to said control switch and to said interrupter means for directing current to said lamp through said interrupter in response to closing of said thermal responsive switch means, said interrupter and said lamp producing a flashing light to act as a visual fire warning.

2. A fire warning device as set forth in claim 1 which also includes means for generating an audible alarm in response to closure of said thermally responsive switch.

3. A fire warning device as set forth in claim 2 which also includes means for manually moving said thermal responsive switch from a normally open to a closed state to test the device for proper operation.

4. In combination with a wall mounted enclosure internally receiving a cable enclosing electrical conductors connected to a light switch controlling a lamp which provides illumination in a room and a switch plate closing said enclosure and having perforations formed therein, means for providing a fire warning comprising:

thermal responsive switch means having a first state when the temperature of the switch is below a fire alarm condition and a second state when the temperature is above an alarm condition;

means mounting said switch means within said enclosure adjacent said switch plate and in alignment with said perforations for exposing said thermal responsive switch means to temperature conditions external of said enclosure;

current actuated interrupter means connected between said electrical conductors and said light switch; and means connecting said thermal responsive switch means to said electrical conductors and said light switch and actuated when said thermal responsive switch is in the first state for forming a conductive path between said light switch and said conductors in parallel with said interrupter to enable the normal illumination of said lamp and actuated when said thermal responsive switch is in the second state for forming a conductive path between said interrupter and said lamp in parallel with said light switch to intermittently illuminate said lamp and visually indicate the existance of a fire warning condition in the room.

5. The combination as set forth in claim 4 which also includes an audible fire alarm connected in parallel with said interrupter to be actuated when said thermal responsive switch is in the second state.

6. The combination as set forth in claim 5 in which said audible alarm includes a cylindrical tube of non-conductive material mounted within said enclosure to position the axis of said tube substantially perpendicular to a wall of the enclosure and one end of the tube spaced from said wall;

a cylindrical shaft of a metal having magnetic susceptability slidably mounted within said tube;

a spring connected to said shaft to bias one end of said shaft into engagement with the wall of the enclosure; and

a coil of wire around said tube and connected in parallel with said interrupter to excite said shaft to strike the wall of said enclosure and generate an audible alarm when said coil is energized.

7. The combination as set forth in claim 4 which also includes means for manually changing said thermal responsive switch from the first state to the second state to test the system for proper operation.

References Cited UNITED STATES PATENTS ROBERT L. RICHARDSON, Primary Examiner US. Cl. X.R. 40-220 

